Means for protection against and/or indication of faults in coreless induction furnaces, heating furnaces and the like



Dec. 3, 1968 MEANS FOR PROTECTION AGAINS CORELESS INDUCT I. BECKIUS TAND/OR INDICATION OF FAULTS IN ION FURNACES HEATING FURNACES AND THELIKE Filed Nov. 29, 1965 INVENTOR. Ivar BzcKlus United States Patent3,414,660 MEANS FOR PROTECTION AGAINST AND/OR INDICATION OF FAULTS INCORELESS IN- DUCTION FURNACES, HEATING FURNACES AND THE LIKE IvarBeckius, Vasteras, Sweden, assignor to Allmiinna Svenska ElektriskaAktiebolaget, Vasteras, Sweden, a corporation of Sweden Filed Nov. 29,1965, Ser. No. 510,245 Claims priority, application Sweden, Dec. 16,1964, 15,196/64 1 Claim. (CI. 13-27) The present invention relates to ameans for protection against and/or indication of faults in a coil orcoils in induction furnaces of coreless crucible type, heating furnacesand the like.

Furnace coils in induction furnaces (for low or high frequency) formelting, or heating furnaces, are subjected to difficult operatingconditions, which are often accompanied by short circuits between thewinding turns of the coil. Such short circuits result in arcs which,when they have been active for a time, usually create holes in thewater-cooled copper tubes of the coil, that is current conductors forthe coil. It has been practically impossible to prevent this because ofthe absence of indication of these faults. The coils have been providedwith insulation, but this has not resulted in the elimination of saiddisadvangages.

The device according to the invention gives a solution to these andother connected disadvantages, in which the coil turns are possiblysurrounded by insulation and around this (or at a distance from, butconcentrically with the conductor) an uninterrupted metal cover whollyor partially enclosing the conductor section and without insulatinginterruption in the longitudinal direction of the current conductors.The device is characterised in that the cover and conductor are joinedat one coil end and joined across a relay and/or a voltage measuringdevice at the other coil end directly or through an insulatingtransformer, so that upon short circuiting or some other insulationfaults between the coil turns the relay is actuated and the furnace feedis disconnected and/or the fault is indicated. Through this meansdisconnection of the feed and/or indication of the fault is carried outquickly, be-

fore further damage to the coil and insulation have developed.

The invention is further clarified in the accompanying figures, of whichFIG. 1 shows a connection diagram of the invention, FIG. 2 a crosssection of the coils with the cover and FIG. 3 an example in crosssection through a coil conductor with completely closed metal cover.

In FIG. 2 a crucible 11 is shown, containing melt or I material to bemelted. The different coil conductors 12-15 ing so that it wholly orpartially covers the conductors. At one end of the coils 12-15 theconductor and cover are joined together (see 18 in FIGS. 2 and 1) whileat the other coil end the joining together is carried out across avoltage measuring device 19 and/ or a relay 20, possibly with anintercoupled insulating transformer (not shown). The relay 20 isarranged to disconnect the furnace feed upon actuation.

The connection of coil protection and coil indication means is evidentfrom FIG. 1. The current conductors of the furnace coil is here denoted21, while as previously the metal cover is denoted 17. The furnacemeasurer is connected at E. Because of different flux directions thevoltages induced by the flux during the operation of the furnace in theconductor 21 and the cover compensate each other, so that the dischargeof the measuring device 19 will be zero during normal operation. It maybe desirable on account of certain differences between the fluxesthrough the cover 17 and the conductor 21 to arrange a compensation coil(not shown) with corresponding flux, with a view to reducing the fluxthrough the conductors in order to obtain full compensation.

Upon a leak between the conductors, short circuiting of two cover turnsis produced and the balance between the indicated voltages in 17 and 21disappears, so that a certain voltage is indicated in the measuringinstrument and thus a fault is indicated. At the same time voltageacross the relay 20 is produced and the furnace feeding is switched off,after which the fault in the coil can be repaired. It is possible toarrange only indication or only use a relay.

This connection (FIG. 1) can also be complemented with a cruciblesupervisory connection according to US. Patent No. 3,185,894.

If the furnace coil is divided up into several part coils, the above canbe applied on each individual part coil.

The invention can also be applied to heat induction furnaces with coilsof water-cooled tubes.

The invention can be varied in many ways within the scope of the claim.

I claim:

1. Means for protection against faults in a coreless induction furnace,said furnace comprising a crucible surrounded by coil turns covered byinsulation, comprising, at least partly around said insulation, anuninterrupted metal cover conducting in the longitudinal direction ofthe current conductor, the conductor of the coil and the metal coverbeing coupled together at one coil end, said conductor and metal coverbeing coupled together at the other coil end across a voltage sensitivemember, said member being affected upon short circuits or otherinsulation faults.

References Cited UNITED STATES PATENTS 1,801,791 4/1931 Breisky et al340-242 2,614,200 10/1952 McNair 219-481 X 2,990,542 6/1961 Seitz l327 X3,185,894 5/1965 Beckius 317-9 3,214,637 10/1965 Persson 317-13 RICHARDM. WOOD, Primary Examiner.

L. H. BENDER, Assistant Examiner.

1. MEANS FOR PROTECTION AGAINST FAULTS IN A CORELESS INDUCTION FURNACE,SAID FURNACE COMPRISING A CRUCIBLE SURROUNDED BY COIL TURNS COVERED BYINSULATION, COMPRISING, AT LEAST PARTLY AROUND SAID INSULATION, ANUNINTERRUPTED METAL COVER CONDUCTING IN THE LONGITUDINAL DIRECTION OFTHE CURRENT CONDUCTOR, THE CONDUCTOR OF THE COIL AND THE METAL